1. Field of the Invention
The invention relates to a memory apparatus and a writing method thereof, and particularly relates to a resistive memory apparatus and a writing method thereof.
2. Description of Related Art
A non-volatile memory has an advantage that data stored therein is not disappeared after power off, so that it serves as a necessary memory element for maintaining a normal operation of many electronic products. Presently, a resistive random access memory (RRAM) is a kind of non-volatile memory positively developed in the industry, which has advantages of low write operation voltage, short write and erase time, long memory time, non-destructive reading, multi-state memory, simple structure and small occupation area, etc., and has a great application potential in personal computers and electronic equipment in the future.
Generally, the resistive random access memory can change a width of a filament path according to magnitude and polarity of an applied pulse voltage, so as to set a resistance value to a low resistance state (LRS) or a high resistance state (HRS) in a reversible and non-volatile manner to respectively represent stored data of different logic levels. For example, when data of logic 1 is written, a reset pulse can be applied to narrow the width of the filament path to achieve the HRS. When data of logic 0 is written, a set pulse with an opposite polarity can be applied to broaden the width of the filament path to achieve the LRS. In this way, when the data is read, the data of logic 1 or logic 0 can be read according to a reading current of a different magnitude generated under different resistance states.
However, when the data of logic 0 is written, the filament path in a variable resistance element may have a sharp contour after the set pulse is applied thereto, such that a filament path with an excessively large width at one end and an excessively small width at another end is formed, which results in a problem of electromigration (EM). To be specific, when a large current continuously flows through the variable resistance element, the narrower a place in the filament path is, the higher a current density at the place is, and the higher an electric field thereof is, which leads to a phenomenon that metal atoms move towards an electron flowing direction along grain boundaries of the variable resistance element itself. As the electromigration is continuously increased, the current density is accordingly increased to aggravate the situation. If the electromigration is too severe, the variable resistance element can be broken to form an open circuit, such that data cannot be correctly written.